1. Field of Invention
The invention relates generally to the field of precision fluid dispensing for Bioscience applications and more particularly to a two-piece pump with a multiple diameter cylinder and piston and multiple inlet and outlet ports that can be controlled by a micro-controlled precision drive system capable of closed loop control.
2. Description of the Problem Solved
Syringe pumps that use glass syringes and pistons with seals are routinely used for fluid dispensing in the Biosciences. Independent valves are usually used to control fluid inlet and outlet functions. Currently, a syringe pump made by Cavro, Kloehn and Hamilton provides various syringe sizes for dispensing in the range of 1 microliter to 50 milliliter. Valve functions provide for multiple inlet and outlet ports. Although the syringe barrel plugs directly into the valve body, using seals, the valve can be essentially separate from the syringe. The syringe area and the piston linear displacement define the dispensed syringe fluid volume. In most cases, a stepper motor that is coupled to a lead screw to translate the rotary to linear motion controls the syringe piston displacement. The stepper motors in high end units often have shaft encoders so as to provide for drive overload detection for motor step loss.
The Cavro XL 3000, for example, with 8-port distribution valve, provides for a linear resolution of either 3000 or 24000 steps or increments in its 60 mm available piston travel. An optical encoded stepper motor also controls the valve stack port positioning. The valve stack can be directly or indirectly coupled to a second stepper motor shaft, and the syringe output end can be inserted into the bottom of the valve stack utilizing a seal.
The Hamilton Microlab 500 fluid diluters and dispensers are also precision fluid measuring instruments based on syringe technology. The Hamilton systems often use two syringe pumps to accomplish diluter functions. Sample dilutions are made by first filling one of the syringes with a programmed amount of diluent from a reservoir followed by aspirating a programmed amount of sample into the end of the dispensing tube using the second syringe. The last step to accomplish the dilution is to dispense the sample and diluent into a vial. Dispensing functions using a two syringe pump Hamilton unit are accomplished by filling one syringe with reagent 1 and the other with reagent 2. The two syringe pumps output the desired ratio into a common tube for vial filling. The syringe pumps are not known to provide reliability for long run cycles due to failure of the piston and cylinder seal and the seals that make up the valve stack. Also, cleaning of the system often requires the operator to completely disassemble the syringe cylinder and piston along with the rotary valve stack. This disables the entire dispensing system. In many applications, individuals completely flush out the dispenser with cleaning solutions rather than dismantle the system.
A simple two-piece pump is known in the art and is usually provided in either stainless steel or ceramic materials. This type of pump consists of a piston and cylinder in which the piston can also provide the valving functions. SPC France, NeoCeram and others manufacture two-piece pumps for the pharmaceutical industry, and recently two diameter pumps providing smaller volume dispensing capability have also appeared on the market.
NeoCeram and others have also built pumps that have multiple ports. The pump does not require moving seals between the piston and cylinder as close tolerances and a fluid provide the sealing function. The piston with a valve slot can be rotated between predetermined positions to select either inlet or outlet ports. When the correct inlet or outlet port has been selected, the linear motion provides for fluid aspiration or dispensing. In special cases, to recover pump fluid at the end of dispensing or for using cleaning fluids, inlet and outlet ports can be aligned. In nearly all cases the two-piece pumps have been designed and developed for high-speed fluid filling manufacturing lines. The drive hardware is expensive requiring precision ground ball screws along with motor encoders. The motor encoders can only detect the motion of the motor and not that of other elements in the drive train to the pump piston.
Syringe type positive displacement pumps are capable of dispensing very small fluid quantities but when the volumes drop below 3 microliters, getting the drop off the tube or nozzle requires contact or very near contact to the dispensing surface. Cartesian Technologies and others have provided active nozzles to simplify small volume delivery for the micro-array market. Cartesian Technologies uses a solenoid valve that is fluid coupled and synchronized to a syringe pump. Other systems use aerosol jet or piezoelectric devices coupled to syringe pumps to assist in small volume dispensing.
What is badly needed is a cost effective, small volume, easily cleanable, precision dispensing system for the Biosciences. A two-piece pump should utilize a piston and cylinder with at least two diameters, multiple inlet and outlet ports, and a precision pump drive system with cost effective electronics to meet these requirements. The pump drive needs to provide accurate dispensing with the position controlled by a linear measurement means. A controller can also provide capability for synchronization with active nozzles along with A/D capability to provide for external sensors to be read, such as a pressure transducer.
The present invention relates to a two-piece pump and a precision closed loop controller drive system to address the small volume precision dispensing requirements of the Bioscience market. The two-piece pump can contain a cylinder and piston with two different diameters to create a sealless pump with integrated valving. The pump cylinder and piston should have more than two diameters or the diameters can be tapered or curved. In a multiple diameter pump the amount of fluid dispensed is related to the difference of the diameter areas times the linear displacement of the piston.
The present invention, combines a multiple diameter pump with a pump having multiple inlet and outlet ports and with a precision control system. The configuration allows for precision multiple outlet dispenses in a single pump that can be used, for example, with microtiter plate pipetting. A positive displacement pump option for microtiter plate dispensing is the use of a pump with multiple inlet and outlet ports. The preferred position of inlet ports on the multi-diameter cylinder is on the smaller diameter part of the cylinder, while the preferred position of outlet ports is on the larger diameter of the cylinder. However, it should be noted that the ports could be located anywhere on the cylinder and still be within the scope of the present invention. The smaller diameter part of the cylinder is usually located at the lower portion of the cylinder relative to the larger diameter portion. The piston can have a groove on the smaller diameter part connected to a groove on the larger diameter part. The number of inlet and outlet ports is limited by the piston/cylinder diameter and the spacing between adjacent ports. If 5 mm were used as a minimum spacing between ports, and the pump has (10) 1 mm ports, where 8 ports are outlet and 2 ports are inlets, the necessary pump diameter would be just over 19 mm in diameter. For 19 mm diameter pump to dispense in the microliter range, the difference in the diameters should be small and the linear drive capable of very small displacements.
One of the preferred pump configurations of the present invention uses a two-diameter, multiple port pump with 2 inlet ports and 8 outlet ports. The pump is also capable of mixing because it can aspirate fluid into the pump from port 1, and then from port 2, followed by rotating the piston to accomplish annular mixing. The piston groove assists in the mixing, but the pump can have other features to assist in mixing as long as none of these features trap air during operation.
For recovery of dispensing fluid, the pump system could use 9 (or any odd number) of outlet ports where the 9th port is aligned with one of the inlet ports. This outlet port could be connected to the fluid supply or other container for recovery. In this configuration, the aligned inlet port could be connected to an air supply which could force remaining fluid out of the aligned outlet port. In another configuration, the aligned inlet and outlet port could be connected to a cleaning or flush solution. The piston could be cleaned by fluid pressure at the inlet port, and the piston could be rotated to clean to clean the fluid boundary layer between the piston and the cylinder. An alternate manufacturing method could be to have the same number of inlet and outlet ports and to plug unused ports in custom configurations.
The precision pump drive can contain at least one stepper motor or DC motor to control the linear motion of the pump piston, and usually another stepper motor or DC motor to control the rotation of the piston. This allows one of the pump""s inlet or outlet ports to be aligned with the piston groove. The linear motion of the piston is generally created by the first stepper motor turning a ball screw. The ball screw nut, if held from rotating will move in a linearly fashion creating the necessary linear motion for the piston. A linear displacement sensor can monitor the position of the piston very accurately, and the entire system can be driven by a closed loop by a micro-controller. The preferred linear sensor for this application is a Renishaw 0.5 micron optical scale or similar scale including magnetic linear scales or linear voltage differential transformers (LVDT). The preferred stepper motors are 5 phase Oriental Nanostepper for the linear motion and 5 phase half step motors for the rotary motion. The Nanostepper motor, as supplied, has (16) discrete resolution ranges from 500 steps per revolution to 125000. These ranges are operator selectable. The use of a nanostepper allows the drive to have an adequate number of steps between the 0.5-micron Renishaw lines. For a THK 4 mm pitch ball screw it would require over 15 steps for the advance of the 0.5 pitch. The resolution can be selectable between inlet and outlet functions. It should be noted that other suitable stepper or DC motors can be used.
As an example, the pump can aspirate fluid into an inlet port at 10,000 steps per revolution and then dispense through an outlet port at 125,000 steps per revolution. Because of the stopped motion stability, simplicity to control and maintain accuracy, the preferred system contains stepping motors. It is also within the scope of the present invention for the linear drive to be a linear motor such as the stepper or DC BALDOR Electric Co. motor or the Nanomotion motor from Nanomotion, Inc.
The pump system can be run orientated in various positions including horizontal and vertical as long as the position allows for air free dispensing. A micro-controller or digital signal processor is preferred to control the rotary and linear positioning. By entering information into the controller as to the desired amount of fluid to dispense, very precise dispensing can be accomplished because the entire resolution of the system is derived from the linear encoder. The movement of the piston can be controlled by several motion velocity profiles including the use of a Gaussian profile for smoothness of motion. To effectively dispense very small volumes, the controller can optionally interface with active nozzles. This interface, when used, can provide for synchronization of the piston functions with that of the active nozzle. The addition of optional analog to digital conversion (A/D) capability lets the system interface with external sources, such as a pressure transducer or other source.